A pneumatic tire is a composite of complex structure of interacting components, each with properties intended for suitable effectiveness. One important component of a tire is a tread which designed to be a running surface of the tire.
For this invention, a tire tread is desired which is has relatively high hardness and abrasion resistance properties in combination with a an acceptable internal heat generation property such as, for example, a hot rebound property.
The hardness property relates to the stiffness of the tire tread. The abrasion resistance property can relate to resistance to tread wear for a tire tread.
The hot rebound property can relate to an ability of a tread of relatively high stiffness to resist internal heat generation, with an accompanying temperature rise, which, in turn, may relate to durability of the tire tread under working conditions.
It is appreciated that an optimization of one physical property usually detracts, or retards, at least one other physical property. Accordingly, there is desire to present a tire tread of relatively high hardness and abrasion resistance properties which also presents an acceptable hot rebound property.
For this invention, it is desired to provide a tire tread of a rubber composition having a balance of relatively high stiffness, or hardness, high abrasion resistance and an acceptable hot rebound properties for a tread rubber having such relatively high hardness and abrasion resistance properties. Such balance of physical properties is achieved, at least in part, by use of a natural rubber-rich tire tread rubber composition, together with cis 1,4-polybutadiene and styrene/butadiene copolymer rubber which is reinforced with a reinforcing filler as a combination of high structure rubber reinforcing carbon black and precipitated silica in which the carbon black is in the majority of the reinforcing filler.
In the description of this invention, the terms “rubber” and “elastomer” where used herein, may be used interchangeably, unless otherwise indicated. The terms “rubber composition”, “compounded rubber” and “rubber compound”, where used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
In the description of this invention, the term “phr” refers to parts of a respective material per 100 parts by weight of rubber, or elastomer. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” may be used interchangeably unless otherwise indicated.
The glass transition temperature (Tg) of an elastomer may be determined by DIN 53445 at a heating rate of 1° C. per minute unless otherwise indicted.